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Explain the underlying principle for the given scientific phenomenon.
The Doppler effect


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The Doppler effect is the phenomenon where sound and light waves appear to change in frequency when they approach or move away from an observer. This occurs because of the change in perceived distance: when an object moves towards the observer, waves appear to pile up and therefore compress the perceived frequency; when moving away, the waves appear to be spread out and therefore decrease the frequency. This is known as the Doppler Effect and is used in many areas of science, including physics, astronomy, and meteorology.